The present invention relates generally to a method of making a nonwoven fabric through hydroentanglement of a staple fiber precursor web, and more particularly to a method of making a nonwoven fabric through hydroentanglement and by treatment with a binder composition which facilitates use of the fabric for buffing applications for finishing metals, marble, plastics, and other materials.
The production of conventional textile fabrics is known to be a complex, multi-step process. The production of fabrics from staple fibers begins with the carding process where the fibers are opened and aligned into a feed stock known as sliver. Several strands of sliver are then drawn multiple times on drawing frames to further align the fibers, blend, improve uniformity as well as reduce the diameter of the sliver. The drawn sliver is then fed into a roving frame to produce roving by further reducing its diameter as well as imparting a slight false twist. The roving is then fed into the spinning frame where it is spun into yarn. The yarns are next placed onto a winder where they are transferred into larger packages. The yarn is then ready to be used to create a fabric.
For a woven fabric, the yarns are designated for specific use as warp or fill yarns. The fill yarn packages (which run in the cross direction and are known as picks) are taken straight to the loom for weaving. The warp yarns (which run on in the machine direction and are known as ends) must be further processed. The packages of warp yarns are used to build a warp beam. Here the packages are placed onto a warper which feeds multiple yarn ends onto the beam in a parallel array. The warp beam yarns are then run through a slasher where a water soluble sizing is applied to the yarns to stiffen them and improve abrasion resistance during the remainder of the weaving or knitting process. The yarns are wound onto a loom beam as they exit the slasher, which is then mounted onto the back of the loom. Here the warp and fill yarns are interwoven or knitted in a complex process to produce yardages of cloth. Once the fabric has been manufactured, a scouring process is necessary to remove the size from the warp yarns before it can be dyed or finished. Currently, commercial high speed looms operate at a speed of 1000 to 1500 picks per minute, where a pick is the insertion of the filling yarn across the entire width of the fabric. Commercial woven fabrics used in the intended application of the instant invention range from 40xc3x9740 to 80xc3x9780 picks per inch. Therefore, these fabrics would be produced at commercial speeds of about 25 to 40 inches of fabric per minute.
In contrast, the production of nonwoven fabrics from staple fibers is known to be more efficient than traditional textile processes as the fabrics are produced directly from the carding process. Nonwoven fabrics are suitable for use in a wide variety of applications where the efficiency with which the fabrics can be manufactured provides a significant economic advantage for these fabrics versus traditional textiles. However, nonwoven fabrics have commonly been disadvantaged when fabric properties are compared, particularly in terms of surface abrasion, pilling and durability in multiple-use applications. Hydroentangled fabrics have been developed with improved properties which are a result of the entanglement of the fibers or filaments in the fabric providing improved fabric integrity. Subsequent to entanglement, fabric durability can be further enhanced by the application of binder compositions and/or by thermal stabilization of the entangled fibrous matrix.
U.S. Pat. No. 3,485,706, to Evans, hereby incorporated by reference, discloses processes for effecting hydroentanglement of nonwoven fabrics. More recently, hydroentanglement techniques have been developed which impart images or patterns to the entangled fabric by effecting hydroentanglement on three-dimensional image transfer devices. Such three-dimensional image transfer devices are disclosed in U.S. Pat. No. 5,098,764, hereby incorporated by reference, with the use of such image transfer devices being desirable for providing a fabric with enhanced physical properties as well as an aesthetically pleasing appearance.
For specific applications, a nonwoven fabric must exhibit a combination of specific physical characteristics. Many material finishing operations require the use of power-driven buffing wheels or belts for buffing and polishing metal, rubber, marble, and plastic surfaces. Buffing wheels typically comprise a hub component to which one or more woven textile elements are secured for contact with the surface to be treated. Woven cotton and polyester/cotton materials have typically been employed since such materials can exhibit the necessary non-abrasiveness, absorbency, heat resistance, low elongation, and dimensional stability. By virtue of the absorbency of such materials, the typical water-based buffing and polishing compounds are absorbed and retained by the fabric, with abrasive grit in the compounds sized to achieve the desired buffing or polishing effect.
Certain disadvantages are associated with the typical use of woven fabrics for buffing applications. In order to employ woven fabrics in buffing applications it is necessary to orient the fabric at a 45xc2x0 angle to minimize fraying during use. This application of xe2x80x9cbias slittingxe2x80x9d requires additional processing by specialized equipment, further complicating buffing wheel manufacture. Furthermore, woven fabrics tend to exhibit poor localized dimensional stability as the strength imparted by the woven structure degrades as a consequence of the repetitive impact and resultant fracturing of the supporting yarns during the stresses imposed by buffing. Additionally, price fluctuations in textile commodities can detract from economical use of such woven fabrics.
Heretofore, attempts to employ nonwoven fabrics for buffing applications have met with limited commercial success. U.S. Pat. No. 5,989,113, hereby incorporated by reference, discloses a buffing tool comprising a spunlaced (hydroentangled) nonwoven fabric. The material contemplated by the referenced patent does not exhibit the desired levels of durability, absorbency or improved buffing properties that can be obtained by the imaged nonwoven fabric of the present invention.
The present invention is directed to a method of making a nonwoven fabric for buffing applications, which fabric exhibits excellent durability as well as absorbency to facilitate economical and efficient use.
A method of making a nonwoven fabric embodying the principles of the present invention contemplates use of staple length polyester fibers to facilitate economical fabric formation. Formation of the fabric on a three-dimensional, image transfer device by hydroentangling imparts desired physical properties to the fabric to facilitate its use in buffing applications. Additionally, treatment of the fabric with a binder composition provides the necessary durability for the fabric for buffing surfaces, including metal, rubber, marble, and plastic.
A method of making a nonwoven fabric in accordance with the present invention includes providing a precursor web comprising polyester staple length fibers. The precursor web is preferably pre-entangled on a foraminous forming surface, preferably through the use of high-pressure water jets.
The present method further entails the provision of a three-dimensional, image transfer device having an array of three-dimensional surface elements thereon. The precursor web is positioned on the image transfer device, and hydroentangled to form an imaged nonwoven fabric having a pattern of apertures therein.
The present invention further contemplates application of a polymeric binder composition to the imaged fabric. Notably, the binder composition comprises a melamine polymeric compound in the range of 0.2% to 0.5% weight to volume, and an acrylic/copolymer compound is the range of 10 to 25% weight to volume, which desirably acts to impart the necessary durability to the imaged fabric. In accordance with the present invention, the resultant fabric has a Combined Tensile Strength of at least about 800 grams per ounce of fabric, and further, has a Taber Abrasion of at least 1000 cycles.
In accordance with one illustrated embodiment, the three-dimensional image transfer device has an array of three-dimensional surface elements having an octagon-and-square configuration. An alternative image transfer device has an array of three-dimensional surface elements having a herringbone configuration. These presently preferred image transfer devices act, through hydroentanglement, to impart a high degree of strength and durability to the nonwoven fabric. Additionally, the forming surface can be configured to form apertures in the nonwoven fabric which desirably act to facilitate thermal dispersion during use of the fabric for buffing applications. It is contemplated that the fabric can be selectively apertured, whereby apertures can be provided at the inner portion of a rotary buffing tool to provide thermal dispersion, while avoiding occlusion of apertures at a peripheral portion of the tool.
In the preferred form, the binder composition not only includes a melamine polymeric compound, but further preferably includes an acrylic/copolymer composition. The polymers of the binder composition cooperate to provide the desired durability for buffing applications. Additionally, this binder composition desirably acts to abate deposition of any polyester residue, which can result from degradation of the polyester fibers from heat generated during buffing.
Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims.